Gamma ray radiation detection (gamma ray detection) is desirable for various applications. As one non-limiting example, methods such as single-photon emission computed tomography (SPECT) and positron emission tomography (PET) detect gamma ray radiation for biomedical imaging.
One method of gamma ray detection employs one or more scintillator detectors that emit a flash of light in response to a gamma ray interaction with the detector. This flash of light is typically detected using photomultiplier tubes (PMTs), which convert the flash of light to electrons for processing by a readout system having suitable circuitry. PMTs, however, can be quite large. This limits portability or availability of some gamma ray detection systems. Further, large amounts of shielding (e.g., lead shielding of 500 pounds or more for some imaging applications) may be required.
On the other hand, solid state detectors increasingly are being used for gamma ray detection. Solid state detectors include a material that directly converts gamma rays to electrons, which electrons can be processed by readout systems coupled to the solid state detectors. Example materials for solid state gamma ray detection include detectors that can convert gamma rays to electrons at room temperature, such as cadmium zinc telluride (CdZnTe or CZT), cadmium telluride (CdTe), and others. CZT and CdTe detectors have been widely used for biomedical imaging applications, for instance.
Such solid state detectors have the potential to offer the combination of excellent energy resolution, good spatial resolution, and at least adequate detection efficiency for gamma rays emitted by common single photon emitters, such as I-125, Tc-99m, I-123, In-111, and TI-201. In recent years, the use of small-pixel CZT or CdTe-based imaging sensors to replace scintillation detectors for high-resolution SPECT imaging applications has been evaluated in the art. There has also been extensive effort in the art towards building positron emission tomography (PET) systems based on CZT and CdTe detectors.
However, certain problems can occur with small-pixel CZT and CdTe detectors designed for ultrahigh resolution gamma ray imaging applications. One problem is that charge (electron) collection efficiency is severely degraded by charge loss and charge sharing effects when the physical dimension of anode pixels approaches the size of the electron cloud created by gamma ray interactions (typically a few hundred microns). These effects depredate the accuracy of energy, depth of interaction (DOI), and timing information that can be obtained from the small anode pixels.
Another problem is that as future detectors are pushing for higher spatial resolutions, smaller and smaller pixels have to be used. This typically leads to a very large number of pixels to be read out and requires highly complex readout circuitry to extract the energy, spatial, and timing information needed for gamma ray imaging applications.